Undefined symbols on macOS with Intel compiler (#628)

The linker on macOS does not include `common symbols` by default.
The top level CMakeLists.txt file was updated to fix this.

Fixes #620.

CMakeLists.txt

@@ -32,6 +32,12 @@ if(CMAKE_Fortran_COMPILER_ID MATCHES "^(Intel)$")
   set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -g -traceback")
   set(CMAKE_Fortran_FLAGS_RELEASE "-O3 -fp-model precise")
   set(CMAKE_Fortran_FLAGS_DEBUG "-O0 -check -check noarg_temp_created -check nopointer -fp-stack-check -fstack-protector-all -fpe0 -debug -ftrapuv")
+  if(APPLE)
+    # The linker on macOS does not include `common symbols` by default.
+    # Passing the -c flag includes them and fixes an error with undefined symbols.
+    set(CMAKE_Fortran_ARCHIVE_FINISH "<CMAKE_RANLIB> -c <TARGET>")
+    set(CMAKE_C_ARCHIVE_FINISH "<CMAKE_RANLIB> -c <TARGET>")
+  endif()
 elseif(CMAKE_Fortran_COMPILER_ID MATCHES "^(GNU)$")
   set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -g -fbacktrace")
   if(${CMAKE_Fortran_COMPILER_VERSION} VERSION_GREATER_EQUAL 10)